During the last decade, intracellular calcium (Ca²⁺_i) transients have been recognized as an important pacemaker mechanism in sinoatrial nodal (SAN) cells. The so called “Ca²⁺_i clock” directly depolarizes the membrane potential through activation of the sodium calcium exchange current (I_NCX)¹. Recent evidence suggests that Ca²⁺_i also indirectly increases the funny current (I_f) through activation of Ca²⁺_i–stimulated adenylyl cyclases (AC1 and AC8)^2,3. In this study we investigated to what extent acetylcholine (ACh) change Ca²⁺_i transients and how these changes affect cAMP and pacemaker frequency. Ca²⁺_i transients were recorded from isolated rabbit SAN cells using Indo-1 fluorescence. Intracellular cAMP was measured in SAN cells using a LANCE^® cAMP 384 Kit and a Victor plate reader. ACh slowed pacemaker frequency (n=13), decreased cAMP (n=15), inhibited all phases of the Ca²⁺_i transient (n=13) and reduced the SR Ca²⁺ content (n=7) in a concentration dependent fashion. On the other hand, noradrenaline (NA) speeded pacemaker frequency (n=22), increased cAMP (n=15) and augmented all phases of the Ca²⁺_i transient (n=22) and increased the SR Ca²⁺ content (n=7). The ACh-mediated changes persisted in the presence of NA, albeit all significantly attenuated. Inhibition of Ca²⁺_i transients by 3 µmol/L ryanodine lowered the basal intracellular cAMP concentration (n=7) and intrinsic pacemaker frequency (n=8). Moreover, ryanodine prevented the NA-mediated increase in cAMP (n=7) and pacemaker frequency (n=10). Furthermore, ryanodine facilitated the ACh-mediated inhibition of cAMP (n=7) and pacemaker frequency slowing (n=10) in the presence of NA. Similar cAMP changes were obtained when Ca²⁺_i was buffered with 25 µmol/L BAPTA-AM (n=3). Here we show that ACh decreases Ca²⁺_i transients, cAMP levels, and pacemaker frequency. In addition, all effects of ACh were attenuated by NA-stimulation. Finally, Ca²⁺_i transients control cAMP production and pacemaker frequency. The latter observation provides an indirect mechanism by which Ca²⁺_i can modulate cAMP-dependent currents, such as I_f, and pacemaker frequency.